NAFO Sci Coun. Studies, 7: 53-59 Feeding of Roundnose Grenadier (Coryphaenoides rupestris) and its Trophic Relationships in the North Atlantic* A. V. Gushchin Atlantic Research Institute of Marine Fisheries and Oceanography (AtlantNIRO) 5 Dmitry Donskoy Street, Kaliningrad, USSR and S. G. Podrilzhanskaya All-Union Research Institute of Marine Fisheries and Oceanography (VNIRO) 17 V. Krasnoselskaya Street, Moscow, USSR Abstract The food spectra of roundnose grenadier from the continental slope areas of eastern Canada. West Greenland. Iceland and Hatton Bank and from the thalassobathyal zones of Reykjanes Ridge and the northern part of the Mid-Atlantic Ridge are compared and changes in feeding by region and fish size are demonstrated. Roundnose grenadier from the continental slope areas of the North Atlantic are shown to be consumers mainly of the second order. their food consisting typically of crustaceans (amphipods, euphausiids, mysids, small decapods and copepods). with fish and cephalopods being generally of much less importance. In the thalassobathyal areas of the North Atlantic. roundnose grenadier are consumers of the third or fourth order. their food consisting mainly of various fish species (myctophids. bathylagids. serrivomerids. chauliodontids and searsiids) and large crustaceans (decap­ ods). The differences are discussed in relation to the environmental conditions and the trophic structures of the communities in the different regions. Introduction eggs and larvae drift in the Irminger Current to West Greenland, from which the young are dispersed by the Roundnose grenadier are found on the slopes of Baffin Land and Labrador Currents to settle off Labra­ the continental shelves throughout the North Atlantic dor and northeastern Newfoundland, and that the mat­ from about 37° N off the United States coast northward uring fish return to the Icelandic area for spawning to Baffin Island, off West Greenland and Iceland, and in (Podrazhanskaya, 1971). The capture of roundnose the Barents Sea (Savvatimsky, MS 1969). They occur in grenadier in the pelagial over great depths (Haedrich, depths generally exceeding 400 m, and USSR investi­ 1974) is indirect evidence of migration opportunities gations in the Northwest Atlantic have shown that for the species. commercial concentrations exist off Newfoundland and Labrador in 500-1.000 m. Recent studies have Despite the opinions of some researchers that shown roundnose grenadier to be part of the ichthy­ grenadiers are poor swimmers due to their body shape ofauna of Reykjanes Ridge and the northern part of the and are unlikely to undertake extensive migrations Mid-Atlantic Ridge (Gushchin and Kukuev, 1981), and (Savvatimsky, 1972; Parsons, 1976), some recent pap­ on the continental slope off Northwest Africa (Golo­ ers support, to a certain degree, the idea of population van, 1978). unity of roundnose grenadier throughout the North Atlantic (Alekseev et al., 1979; Marti, 1980; Zubchenko, Various aspects of the biology of roundnose gren­ 1981). In this paper, with the use of data on feeding of adier have been studied, e.g. age and growth by Savva­ roundnose grenadier in various regions, an attempt is timsky (1971,1972), parasites by Zubchenko (1981), made to show the position of the species in the trophic reproduction by Grigorev (1972) and Geistdoerfer system of the North Atlantic. (1979), and food and feeding by Podrazhanskaya (1971), Konstantinov and Podrazhanskaya (1972) and Gushchin (1982a). Conflicting hypotheses have Materials and Methods evolved from these and other studies on the extent of migrations and the population unity of roundnose The data in this paper were derived from analyses, grenadier in the North Atlantic. The absence of sexu­ by the authors and their colleagues, of the stomach ally mature individuals in Northwest Atlantic catches contents of roundnose grenadier which were collected from depths to 1,000 m and the discovery of spawning at different times by USSR research vessels in various grounds south of Iceland have led to the opinion that areas of the North Atlantic (Fig. 1). The laboratory • Based on a paper presented at the NAFO Special Session on "Trophic Relationships in Marine Species Relevant to Fisheries Management in the NorthWest Atlantic", held at Leningrad. USSR. 14-16 September 1983. 54 Sci. Council Studies, No.7, 1984 A • Hatton North Reykjanes Ridge • B South Reykjanes• Ridge c Gibce• Fracture o 3L • North Mid-Atlantic• Ridge Fig. 1. The North Atlantic region showing the locations of round nose grenadier samples used in this paper. analyses involved 1,371 specimens from the Northwest by field analysis (incidence of food items) of large Atlantic in areas extending from West Greenland and numbers of stomachs from the Northwest Atlantic Baffin Island to the northern slope of Grand Bank off (>13,000) and from the Reykjanes Ridge and northern Newfoundland, 261 specimens from continental slope Mid-Atlantic Ridge in the Northeast Atlantic (>100,000 areas of the Northeast Atlantic (Iceland and Hatton specimens) (Podrazhanskaya, 1968, 1969, 1971; Kon­ Bank), and 1 ,330 specimens from Reykjanes Ridge and stantinov and Podrazhanskaya, 1972; Gushchin, northern Mid-Atlantic Ridge. 1982a). Also, the feeding relationships of deepwater ichthyofauna have involved the field (>8,600 speci­ The roundnose grenadier samples were examined mens) and laboratory (154 specimens) analyses of according to traditional methods of studying feeding stomachs of other fishes whict1 inhabit the same depth relationships in fishes (Borutskiy, 1974). At sea, the ranges and areas as roundnose grenadier in the North specimens without broken tails were measured as total Atlantic (Konstantinov and Podrazhanskaya, 1972; length in centimeters and weighed in grams, the Gushchin, 1982b). This paper incorporates informa­ degree of stomach fullness was estimated by the tradi­ tion from those studies in evaluating the feeding rela­ tional method used by Podrazhanskaya (1968, 1971), tionships between roundnose greandier and other and the stomachs were extracted and preserved in 4% species. formalin for laboratory analysis. The samples con­ tained specimens which ranged in length from 8 to 110 cm and had gonads at all maturity stages of the repro­ Results ductive cycle. In the laboratory, each stomach was weighed, and the food items were separated into iden­ Food composition by area tifiable components and weighed to the nearest 0.1 g. For analysis by area and fish size, the weights of the Northwest Atlantic slope areas. From the sampling various food components were expressed as percen­ of roundnose grenadier in various parts of the region, tages of the total weight of all food in the stomachs from Baffin Island and West Greenland southward to containing food. The total feeding index was calcu­ the Grand Bank, representatives of 74 different taxa lated as the ratio of total weight of food to total weight belonging to nine major groups of invertebrates and of fish sampled, multiplied by 10,000 (expressed as four families of fishes were found in the stomachs 0/000 ) . (Table 1). Empty stomachs generally constituted less than 30% of those examined from the various areas, In addition to the data summarized in this paper, except in Div. 3K and 3L where 66 and 81 % respectively the feeding of roundnose grenadier has been studied were empty, the latter value being based on a very GUSHCHIN and PODRAZHANSKAYA: Feeding of Roundnose Grenadier 55 TABLE 1. Food composition of roundnose grenadier (% by weight) from various areas of the North Atlantic. (See Fig. 1 for locations of areas sampled.) Northwest Atlantic areas Northwest Atiantic slope areas Slope areas Thalassobathyala. Stomach contents o 2G 2H 2J 3K 3L Iceland Hatton A B C D Cephalopoda 5.4 8.7 9.4 2.9 8.2 3.3 1.1 2.6 9.0 7.0 24.6 4.3 5.5 Chaetognatha 0.6 1.8 1.3 5.8 2.4 0.2 0.3 0.2 0.0 0.1 0.0 Polychaeta 2.5 0.3 0.8 0.1 1.5 0.0 0.0 0.0 0.0 Scyphozoca 8.9 4.0 1.7 3.5 Tunicata 1.9 1.2 0.9 1.3 3.1 0.8 0.3 0.3 0.1 0.1 Crustacea 85.0 70.9 53.0 84.3 57.8 91.5 27.3 88.1 76.3 14.5 18.7 36.2 23.7 Amphipoda 49.0 28.2 35.9 76.6 25.4 3.8 0.4 1.0 0.8 0.6 1.3 0.1 Copepoda 5.1 1.6 8.5 0.8 6.6 1.5 4.6 0.1 0.5 0.1 0.2 1.3 0.3 Decapoda 4.4 12.9 2.1 2.3 13.2 84.5 18.5 51.4 55.9 7.8 12.7 19.8 18.9 Eu phausiacea 5.4 9.8 6.5 4.6 12.6 1.7 35.5 0.4 1.2 0.4 0.4 Isopoda 0.1 0.0 0.4 0.1 Mysidacea 21.1 18.4 0.0 3.8 0.1 11.9 3.1 3.1 8.4 3.2 Ostracoda 0.4 0.3 0.3 0.0 Unidentified 7.5 2.3 0.6 4.3 0.7 Pisces 6.5 8.3 30.5 2.7 28.8 0.8 70.2 4.8 12.2 67.5 52.1 57.0 66.0 Bathylagidae 28.4 7.9 1.7 8.8 Chauliodontidae 3.4 2.5 5.4 4.0 Cottidae 2.8 Malacosteidae 5.8 5.8 Melamphaidae 2.0 1.9 3.5 0.9 Myctophidae 2.1 22.6 0.3 1.6 69.6 12.2 10.4 8.8 10.6 28.6 Paralepididae 10.9 Scorpaeidae 0.6 7.2 Searsiidae 4.3 1.5 11.8 Serrivomeridae 7.9 19.0 18.3 1.8 Unidentified 3.8 5.5 7.9 2.4 18.0 0.8 0.6 4.8 6.5 7.7 10.2 4.3 Unidentified food 8.1 3.8 3.3 1.1 1.4 3.4 2.5 1.6 0.3 0.6 1.2 Total stomachs 727 156 97 79 125 172 15 236 25 578 255 338 159 Empty stomachs (%) 29.2 25.6 24.7 18.9 8.8 66.3 81.0 6.8 40.0 44.2 14.2 27.2 17.0 Feeding index (0/000) 64 28 20 34 35 7 20 43 36 35 39 27 32 a A = North Reykjanes Ridge, B = South Reykjanes Ridge, C = Gibce Fracture, D = North Mid-Atlantic Ridge.